1. Field of the Invention
This invention relates to an exhaust gas recirculation system for a V-type engine mainly mounted on a vehicle.
2. Description of the Prior Art
In order to increase engine output, the volumetric efficiency must be improved. The volumetric efficiency can be effectively improved by reducing curvature in the intake passage to reduce intake resistance and/or by separating the intake passages for the respective cylinders and elongating the intake passages to make the best use of so-called intake inertia.
However in the case of engines for a vehicle which must be accommodated within a limited space in the engine room, especially in the case of cumbersome V-type engines having a pair of cylinder banks, it is very difficult to provide separate intake passages having a sufficient length and reduced curvature. Therefore, it has been often in the V-type engines that the volumetric efficiency is sacrificed.
In a V-type engine proposed in U.S. Pat. No. 3,303,832 (particularly in FIGS. 1 and 2 thereof), a pair of common passages are provided above the respective cylinder banks to extend in parallel to the crankshaft, and intake passages for the cylinders in one cylinder bank are provided to separately diverge from the common passage above the other cylinder bank so that the intake passages for the cylinders in the pair of cylinder banks extend across each other. With this arrangement, intake passages having a desired length and reduced curvature can be separately provided to effectively improve the volumetric efficiency, thereby improving engine output.
However the V-type engine disclosed in the United States Patent has problems with recirculation of exhaust gas that in order to send back exhaust gas into intake gas to control emission, an exhaust recirculating passage must be connected to each intake passage, thereby significantly complicating piping, and it is very difficult to uniformly distribute recirculated exhaust gas to the cylinders. When the recirculated exhaust gas is not uniformly distributed to the cylinders, combustion in the cylinders changes from cylinder to cylinder.
In Japanese Unexamined Utility Model Publication No. 53(1978)-35318, there is disclosed an exhaust gas recirculation system for an in-line type engine which is directed to improving distribution of the recirculated exhaust gas. However, if the system is directly applied to a V-type engine, a recirculation pipe must be provided for each cylinder bank to complicate the structure.